According to the 3GPP (3rd Generation Partnership Project), any signaling in a transport network which is transport related needs to be AAL2 (asynchronous transfer mode (ATM) adaptation layer type 2) signaling to be 3GPP compliant. That is, a 3GPP compliant network is based on AAL2 switching.
The ITU-T recommendation Q.2630 of the International Telecommunication Union defines an AAL2 path as an ATM VCC (virtual channel connection—consisting of one or more virtual channel links VCL) between two adjacent AAL2 nodes. This ATM VCC can be a SVC (switched virtual circuit), a SPVC (smart/soft permanent virtual circuit) or PVC (permanent virtual circuit). According to this definition, the AAL2 path has only local significance in the interface between two adjacent AAL2 switches. Because of this local significance, there are no guarantees in which way an AAL2 connection traverses through a concatenation of AAL2 paths, i.e. which of the AAL2 paths contribute to the concatenation.
Moreover, the existing definitions of an AAL2 connection and an AAL2 path in the ITU-T Recommendations allow each intermediate AAL2 node, as part of the routing function, to multiplex AAL2 connections of different origins into the same outgoing AAL2 paths.